Last last night while working on my development instance of M2.3 I ran php /bin/magento setup:di:compile and then immediately started to see major performance issues I hadn't previously had.
for example cron jobs started backing up because they were taking too long to run, api calls that previously ran in 250ms now took up to 1m+
I went round in circles for ages, trying all sorts of different things but nothing seemed to help, running c:f, setup:upgrade, turning all the cache off and then on again, trying default mode and developer mode.
Performance has improved slightly now but it's still significantly slower than previous to running compile. I can sometimes now get api responses in similar times as before but then subsequent calls will go back up to the 1700ms range.
Ideas?